This invention relates to a traction apparatus and especially but not exclusively to a traction apparatus for use in a down hole tool which is adapted for operation in horizontal wells or bores.
Within the oil and petroleum industry there is a requirement to deploy and operate equipment along bores in open formation hole, steel cased hole and through tubular members such as marine risers and sub-sea pipelines. In predominately vertical sections of well bores and risers this is usually achieved by using smaller diameter tubular members such as drill pipe, jointed tubing or coiled tubing as a string on which to hang the equipment. In many cases the use of steel cable (wire line), with or without electric conductors installed within it, is also common. All of these approaches rely on gravity to provide a force which assists in deploying the equipment.
In the case of marine pipe lines which are generally horizontal, xe2x80x9cpigsxe2x80x9d which are basically pistons sealing against the pipe wall, are used to deploy and operate cleaning and inspection equipment, by hydraulically pumping them along the pipe, normally in one direction.
Within the oil and petroleum industry to date the requirement to deploy equipment has been fulfilled in these ways.
However, as oil and gas reserves become scarcer or depleted, methods for more efficient production are being developed.
In recent years horizontal drilling has proved to enhance greatly the rate of production from wells producing in tight or depleted formation. Tight formations typically are hydrocarbon-bearing formations with poor permeability, such as the Austin Chalk in the United Stated and the Danian chalk in the Danish Sector of the North Sea.
In these tight formations oil production rates have dropped rapidly when conventional wells have been drilled. This is due to the small section of producing formation open to the well bore.
However when the well bore has been drilled horizontally through the oil producing zones, the producing section of the hole is greatly extended resulting in dramatic increases in production. This has also proved to be effective in depleted formations which have been produced for some years and have dropped in production output.
However, horizontal drilling has many inherent difficulties, a major one being that the forces of gravity are no longer working in favour of deploying and operating equipment within these long horizontal bores.
This basic change in well geometry has led to operations which normally could have been carried on wire line in a cost effective way now being carried out by the use of stiff tubulars to deploy equipment, for example drill pipe and tubing conveyed logs which cost significantly more than wire-line deployed logs.
Sub-sea and surface pipeline are also increasing in length and complexity and pig technology does not fully satisfy current and future needs. There is currently a need for a traction apparatus which can be used effectively in down-hole applications including horizontal bores.
According to the present invention there is provided traction apparatus comprising: a body from which body extends at least one traction member wherein said at least one traction member is adapted to be urged against a traction surface against which traction is to be obtained, and wherein when said at least one traction member is urged against such a surface it is adapted to move relatively freely in one direction with respect to said surface, but substantially less freely in the opposite direction.
Preferably, said at least one traction member is formed from a resilient material.
Preferably, said at least one traction member includes an end portion for contact with a traction surface.
Preferably, said body is elongate and said at least one traction member is adapted to be inclined so that it extends in a first axial direction of the body as it extends between the body and a traction surface.
Preferably, the direction in which the traction member is adapted to move preferentially is substantially opposed to the first axial direction of the body.
Preferably, the system is for use in a bore and the traction surface comprises the inner wall of the bore.
Preferably, there is provided means to move the at least some portion of one or more of at least one traction members with respect to the traction surface.
Preferably, said motion of the one or more traction members allows propulsion of the body with respect to the traction surface.
Preferably, said propulsion is substantially in the direction in which the traction member moves preferentially with respect to the traction surface.
Preferably, the motion of the one or more traction members is provided by applying a force with a component substantially parallel to the direction of preferential movement of the at least one traction member.
Preferably, the motion of the one or more traction members is provided by applying a force with a component substantially perpendicular to the direction of preferential movement of the at least one traction member.
Motion may be provided to the one or more traction members by connection to a rotary member having a first axis, which rotates about a second axis which is not coincident with said first axis.
Preferably, said means to move the at least one traction member comprises means to oscillate said at least one traction member.
Preferably, there are provided a plurality of traction members in close proximity to each other, to form a discrete area of traction members.
Preferably, at least two of the traction members in said discrete area are encapsulated together in a matrix of resilient material.
Preferably, there are provided a number of spaced apart, discrete areas of traction members.
Preferably, at least two discrete areas of traction members are moved relative to each other.